The present invention relates to an electrochemical measuring device comprising an essentially planar sensor substrate with at least one electrochemical sensor, and a cover part in which a tunnel-shaped flow or measuring channel is formed, at least one guiding groove being provided in parallel with the flow channel, and a sealing element which is positioned between the sensor substrate and the cover part to seal the flow channel, said sealing element featuring guiding bodies along its long side, at least one of which guiding bodies projects into the guiding groove of the cover part, and narrow sealing lips bounding the flow channel being an integral part of the sealing element.
For diverse reasons, such as minimization of costs, miniaturization or automation, the measuring device often includes a plurality of sensors which are positioned on a planar sensor substrate. The advantage of this arrangement is that thin film or thick film techniques may be employed to produce the sensitive regions of the sensors and their contact leads.
If this kind of sensor substrate with the sensors disposed thereon is designed for integration into a flow channel, the flow channel must be formed above the planar sensor substrate with the use of a further part, the arrangement usually resulting in a tunnel-shaped cross-section of the flow channel.
If several such measuring devices are to be used side by side or if such a measuring device is to be inserted in an analyzer, where corresponding means are provided for sample inlet and outlet, the problem will arise that as a rule a sample channel of circular cross-section must be connected to a flow channel of tunnel-shaped cross-section.
This problem is aggravated by the necessity of providing a seal between the sensor substrate and the upper part or cover forming the actual flow channel. Seals can be achieved in various ways.
In U.S. Pat. No. 5,520,787, for example, a flow cell is described, which is bounded by two essentially flat plates, where the individual parts are bonded to each other by means of an adhesive. In between the two plates a spacer is disposed which is made of sealing material. A groove in the spacer is designed to provide the flow channel. A disadvantage of this configuration is that the accurate position of the lateral edge of the flow channelxe2x80x94and hence the filling volumexe2x80x94is not defined. In addition, contact between the adhesive layer and the medium to be determined or the sensors cannot be excluded. With certain measuring processes or test media such contacts are highly undesirable. Furthermore, adhesive vapors during the production process may constitute a serious hazard for the quality of the sensors.
Furthermore, the individual parts of the measuring device may be thermally sealed. This may also be criticalxe2x80x94especially in the instance of heat-sensitive substances in the sensor (enzyme sensors, for example). Use of a thermal sealing technique may moreover interrupt or destroy all conductive paths located at a right angle to the flow channel. This implies that thermal sealing techniques can only be used if the sensors are contacted via through-holes from below, which will require considerable manufacturing efforts.
Using an elastomer seal as disclosed in EP 0 690 134 A, for example, has proved to be a more suitable method. It includes an electrochemical flow cell in which a measuring chamber is formed by a recess in a structural part, which is covered by an electrode plate on the opposite side. For sealing purposes a seal element with an opening is provided, the opening essentially corresponding to the recess forming the measuring chamber. These parts are contained in a multi-piece housing which is finally sealed. Two sides of the sealing element carry a bulged rim projecting into a recess on the housing containing the flow cell. For assembly of the flow cell it is a disadvantage that the seal is not held in a defined position in the upper part of the housing before the sensor substrate is inserted. Moreover, it is not fixed in position in the region of sample inlet and outlet.
An electrochemical measuring device of the above kind is disclosed in EP 0 846 947 A. An oblong sealing element is described, which is designed for lateral sealing of a flow channel, and which exhibits a narrow sealing lip extending around the side of the flow channel, whose thickness is about 150 xcexcm, so that only a very small portion of the surface of the flow channel is bounded by an elastomer part. The position of the seal is precisely defined by means of lateral guiding bodies, which project into corresponding guiding grooves formed in the cover part in parallel with the flow channel. A rib pressing the sealing lips against the sensor substrate is molded integral with the cover part both on the long and short sides of the sealing element and will result in discontinuities in the shape of the flow channel in the region of the sample inlet and outlet.
It is an object of this invention to further develop an electrochemical measuring device based on the device described above in such a way that an optimum shape of the flow channel will be achieved inside the measuring device while ensuring optimum alignment of the seal and satisfactory positioning of the sealing lips.
According to the invention this object is achieved by proposing that each of the short sides of the sealing element have a guiding body projecting into a recess in the sensor substrate, which guiding bodies are disposed on that side of a sealing plane defined by the sealing lips, which faces away from the cover part. As the guiding grooves cannot be completely relocated to the sensor substrate due to the fact that the existence of a groove would not permit producing the electrical leads by means of planar large-scale production techniques, the invention provides that at least those guiding bodies be relocated to the other side of the sealing plane, which are positioned in the region of the sample inlet or outlet. By configuring the short sides of the sealing element as defined by the invention the axis of sample inlet and outlet can be brought closer to the surface of the sensor substrate, so that the step between the tunnel-shaped cross-section of the flow or measuring channel and the circular cross-section of the sample inlet and outlet will be advantageously reduced. In this way a more homogeneous shape of the cavity will be achieved, which will greatly reduce the formation of air bubbles and facilitate cleaning of the sample channel.
An enhanced variant of the invention provides that two longitudinal guiding bodies be used, which are disposed on the side of the sealing plane facing towards to the cover part, and both ends of which have moulded-on projections pointing towards the axis of the sample channel, which overlap at least partially the guiding bodies positioned on the short side of the sealing element. This will lead to a robust sealing element which during assembly of the measuring device can simply be held in place in the corresponding guiding grooves of the cover part. In this variant a third longitudinal guiding body of the sealing element can be provided on the opposite side of the sealing plane, which will project into a guiding groove in the sensor substrate.
The invention further provides that the inlet and outlet means for the sample medium be positioned between the projections on the ends of the longitudinal guiding bodies.
According to another variant of the invention two longitudinal guiding bodies of the sealing element are positioned on opposite sides of the sealing plane, one guiding groove for one longitudinal guiding body being disposed in the sensor substrate in parallel with the axis of the flow channel.